Cold-cathode discharge ion pump



Oct. 20, 1970 w, K R 3,535,054

COLD-CATHODE DISCHARGE ION PUMP Original Filed May 25, 1959 3 Sheets-Sheet 1 PRIOR ART PR/0R AR 5 PRIOR ART INVENTOR Oct. 20, 1970 Original Filed May 25'. 1959 4 PRIOR ART 00;. a; He.

W M. BRUBAKER COLD-CATHODE DISCHARGE ION PUMP 3 Sh eecs-Sheet 2 Oct ,1970 f w. M. BRUBAKER 3,535,054

COLD-CATHODE DISCHARGE ION PUMP Original Filed May 25, 1959 5 Sheets-Sheet 5 INVENTOR 3,535,054 COLD-CATHODE DISCHARGE ION PUMP Wilson M. Brubaker, Arcadia, Calif., assignor, by mesne assignments, to The Bendix Corporation, Detroit, Mich., a corporation of Delaware Original application May 25, 1959, Ser. No. 815,352.

Divided and this application Dec. 3, 1963, Ser.

Int. Cl. F04b 19/00; F041= 11/.00

U.S. Cl. 417-48 24 Claims ABSTRACT OF THE DISCLOSURE An ion pump is described in which a cold cathode ion discharge is formed between an anode and a pair of opposed collectors within a pump casing. A replacement material electrode is positioned between the anode and each of the collectors so that material is sputtered from the electrode and deposited on the collectors by a portion of the ions in the discharge.

This application is a division of patent application Ser. No. 815,352, filed May 25, 1959, by Wilson M. Brubaker and Clifford E. Berry.

This invention relates to ion pumps of the cold-cathode discharge type. More particularly, the invention relates to an improved cold-cathode discharge ion pump. The invention is particularly useful for evacuating noble gases and other generally nonreactive ions.

Ion pumps may be generally classified into hot cathode types and cold-cathode discharge types. U.S. Pat. No. 2,850,225, issued Sept. 2, 1958 to R. G. Herb, relates to a hot cathode ion pump. A pump of the type referred to in U.S. Pat No. 2,850,225 is sold by Consolidated Vacuum Corporation, the assignee of the present application, under the trade name Evapor-Ion. Such pumps are generally of high capacity, but have the relative disadvantage of being somewhat bulky and expensive.

A cold-cathode discharge device for measuring the pressure in an evacuated space is described in U.S. Pat. No. 2,197,079, issued Apr. 16, 1940, to Frans Michel Penning. The Penning device consists essentially of a ring anode contained between two cathodes within an evacuated envelope. The anode and cathodes are immersed in a strong magnetic field. A high positive potential with respect to the cathode is applied to the anode. The gas between the anode and cathodes is ionized, allowing a current flow therebetween. The magnitude of the ionization current indicates the pressure existing between the anode and cathodes. Such a vacuum measuring device has the disadvantage of disturbing the vacuum to be measured, as ions are pumped from the evacuated space into the surface of the cathode of the device where they are collected. The vacuum to be measured is thereby over the vacuum which would otherwise exist.

A practical vacuum pump can be made by combining a number of such Penning cold-cathode discharge devices into a single unit. A description of such a pump is contained in Science, vol. 128, pp. 282-284, published Aug. 8, 1958. A pump comprised simply of a plurality of Penning cold-cathode discharge devices suffers from a poor noble gas evacuation characteristic, in that the evacuation pressure obtained by use of such a pump when pumping noble gases oscillates instead of remaining constant. The poor noble gas evacuation characteristic of such a pump results from the inability of the pump surfaces to getter the ions of noble gases pumped thereinto. By getter is meant to establish physical or chemical bonds between atoms and molecules of the pump surfaces and the ions removed from the gas. The failure of the United States Patent O- Patented Oct. 20, 1970 pump surfaces to getter the ions of noble gases is due to the nonreactive nature of such ions.

Nonreactive ions, when driven to the surfaces of the ion pump by the fields of force existing therein, are entrapped physically in the outermost molecular layers of the pump surfaces. This entrapment consists of the ions being driven beneath the surface molecular layers of the pump so as to be physicall retained by the enclosing molecular layers. No appreciable physical or chemical bonding exists between the entrapping molecular layers and nonreactive ions so entrapped. However, the en trapped ions are substantially neutralized during entrapment.

The neutralization of the entrapped ions changes the entrapped ions into entrapped atoms of the nonreactive substances. If the entrapping molecular layers are removed, these nonreactive atoms return to the evacuated area since no bonding exists. Return of the nonreactive atoms to the evacuated area causes a rise in the pressure existing within the evacuated area, because of the addition to the evacuated area of the atoms formerly entrapped.

Entrapped atoms are freed from entrapment by a process known as sputtering. By sputtering is meant the ejection of particles of a surface in various directions from the surface. Sputtering is caused by the bombardment of the surface being sputtered by ions traveling at a high velocity. As the pump surfaces are sputtered, the molecular layers of surface material entrapping the nonreactive atoms are worn away. The nonreactive atoms thereup escape back into the evacuated area.

The oscillatory nature of the nonreactive ion pumping characteristic of conventional cold-cathode discharge ion pumps is apparentl due to a cumulative or avalanche effect in sputtering. When the surface molecular layers have entrapped all of the nonreactive atoms which they are capable of holding, further ion bombardment frees collected atoms from the portions of the surfaces they strike. The freeing of these atoms has two immediate effects. First, the pressure in the evacuated area rises in relation to the number of atoms freed. Second, the increase in the number of atoms in the evacuated area increases the sputtering rate of the collector surfaces, since more ions are availavle these surfaces.

An increase in the sputtering rate of the ion collectioning surfaces frees nonreactive atoms entrapped therein at a faster rate. The pressure within the evacuated area therefore continues to rise until the rate of removal of nonreactive atoms from the collector surfaces due to sputtering no longer exceeds rate at which the collector surfaces are able to entrap nonreactive ions. Thereupon, the collector surfaces again entrap the bombarding nonreactive ions until the entrapment capacity is reached. Further nonreactive ion bombardment thereupon commences to free entrapped nonreactive atoms at a rate faster than the rate at which other nonreactive ions are entrapped, repeating the above described process. Thus, the oscillatory nonreactive ion evacuation characteristic of the conventional cold-cathode discharge ion pump is not due to an inability to pump nonreactive ions into the collector surfaces of the device, but is rather due to an inability of the collector surfaces to retain such ions pumped thereinto.

According to the present invention, the oscillatory noble gas or other nonreactive ion evacuation characteristic of cold-cathode discharge ion pumps is eliminated by depositing the replacement material on the sputtered portions of the collector surfaces, into which the nonreactive ions are being pumped. This deposited replacement material provides additional entrapping capacity for the sputtered collector surfaces.

A pump constructed according to the present invention ice has at least one anode, at least one collector, and a replacement material sputtering source positioned adjacent each collector, all within an evacuated envelope. Particles of replacement material from the replacement material source are sputtered onto the collector surfaces, preferably at a rate at least substantially equal to the rate of over-all loss of material from the collector due to sputtering, thereby maintaining the entrapping capacity of the pump.

The invention may be more readily understood by reference to the accompanying drawing in which:

FIG. 1 is an elevation of a Penning cold-cathode discharge device;

FIG. 2 is a sectional plan view, partially broken away, of a known ion pump consisting of a plurality of Penning cold-cathode discharge devices;

FIG. 3 is an elevation, partially in section, taken along line 33 of FIG. 2;

FIG. 4 is a graph showing the oscillatory evacuation pressure characteristic of the ion pump of FIG. 2 when evacuating argon;

FIG. 5 is a sectional elevation of an improved coldcathode discharge ion pump according to one embodiment of the invention, in which material is sputtered from sputter-cathodes and deposited on sputtered portions of the collectors;

FIG. 6 is a graph showing the improved evacuation pressure characteristic of the pump of FIG. 5;

FIG. 7 is a cross section of another embodiment of the invention utilizable with magnetic fields which are uniform over a long distance in a direction parallel to the field, in which material is sputtered from sputtercathodes and is deposited on sputtered portions of the collector; and

FIG. 8 is a sectional elevation of another embodiment of the invention in which the collectors have transparent portions along the axis of the discharge and the sputtercathode is positioned adjacent these transparent portions.

Referring to FIG. I, the Penning cold-cathode discharge device consists of an evacuated envelope containing an anode 21 and two collector-cathodes 22. The anode 21 is connected by a lead 23 to a high voltage terminal 24 extending through the evacuated envelope. The two collector-cathodes 22 are connected by a common lead 25 to a cathode terminal 26 extending through the evacuated envelope. An electro-magnet 27 creates a magnetic field between the anode 21 and the collector-cathodes 22. An inlet 28 connects the device to an evacuated space.

The anode 21 has a ring configuration so that electrons may pass through the anode with a relatively small chance of striking the anode surface. The collector-cathodes '22 are of solid construction, so that ions reaching the collector-cathodes will strike their surfaces. A high positive potential from a high voltage source (not shown) is applied to the anode terminal 24, and the cathode terminal 26 is grounded through a common connection (not shown). Electrons in the evacuated envelope 20 will therefore tend to move toward the anode due to the attraction between the positive potential of the anode and the negative electron charge.

As an electron tries to approach the anode 21, the magnetic field set up by the magnets 27 is such that the electrons spiral between the anode and collector-cathodes rather than continue to move directly toward the anode. During this spiralling process, the electrons produce ionization in the area of the magnetic field by striking free molecules and atoms of the gas contained in the envelope. These ions are attracted to the collector-cathodes 22 and, upon striking one of the collector-cathodes, impinge in the surface molecular layers of the collectorcathode. The removal of thesse ion from the gas phase in the evacuated envelope therefore reduces the pressure within the envelope.

FIG. 3 shows an elevation, partially in section, of the ion pump of FIG. 2. Two collector-cathodes 34 are adjacent the upper and lower surfaces of the anode 30. A cathode terminal 35 passing through the evacuated envelope 31 is connected to the two collector-cathodes 34 by a connecting lead (not shown). An inlet 36 is connected to the collector-space to be evacuated.

The collector-cathodes are constructed of a reactive material; for example, titanium, magnesium, aluminum, molybdenum or various of the rare earths may be used. A positive potential with respect to the collector-cathodes of approximately 3,000 volts is applied to the anode 30 by means of the high voltage connector 33.

A gaseous discharge, occurirng in the same manner as described above with respect to the Penning device, is initiated. The ions produced by the gaseous discharge are driven into the collector-cathode surfaces and entrapped under the surface molecular layers thereof. Some of the reactive ions are gettered by physical or chemical bonding with atoms and molecules of the collector-cathode material.

Due to the high potential difference between the anode and the collector-cathode, ions strike the collector-cathode with a relatively great velocity. Therefore, material on the surface of the collector-cathodes is sputtered therefrom in the general direction of the anode and the opposite collector-cathode. The removal of material from the collector-cathode surface exposes the entrapued nonreactive atoms in the next succeeding molecular layer. These entrapped atoms are thereby permitted to escape.

A portion of the material sputtered from one collectorcathode is deposited on the opposite collector-cathode. Sputtered material is also deposited on the anode and on the envelope walls. Consequently, the rate of removal of material from a collector-cathode due to sputtering exceeds the rate of deposit on the collector-cathode of material sputtered from the opposite collector-cathode, resulting in an over-all loss of collector-cathode material. Thus, it is apparent that after a short period of operation, the oscillatory pumping characteristic occurs when nonreactive ions, for example, of a noble gas, are being pumped.

FIG. 4 is a graph of the actual pressure measured in a pump of the type illustrated in FIGS. 2 and 3 when pumping argon, a noble gas. A positive potential of 3,000 volts with respect to the collector-cathode is applied to the anode. The pressure within the evacuated envelope varies from a minimum of 0.75 X10 mm. Hg to a maximum of 2.5 10 mm. Hg. The periods between maximum pressure peaks are approximately six minutes.

FIG. 5 shows an improved cold-cathode discharge ion pump according to the invention. An evacuated envelope 50 contains a pair of collector electrodes 51 and a cellular anode 52. A collector electrode terminal 53 passes through the evacuated envelope 50 and is connected to the two collector electrodes 51 by a connecting lead (not shown). Neither the collector electrodes nor the anode need be constructed of reactive material. An anode lead 54 connects the anode 52 to a high voltage connector 55. A pair of cellular replacement material elements 56 which function as sputter-cathodes are positioned between the anode and the collectors. As shown in FIG. 5, there are nine sputter-cathode cells for each anode cell, preferably aligned as shown so that the center of the anode cell is in alignment with the center of a sputter-cathode cell. A sputter-cathode lead 57 connects the sputter-cathodes 56 to a bias terminal 58 passing through the evacuated envelope 50. An inlet 5? connects the device to the space to be evacuated.

The sputter-cathodes are constructed of any material which will sputter satisfactorily. It is not essential that the sputter-cathodes 56 be constructed of reactive material, such as titanium. However, when evacuating gases which may be gettered, it is preferable to use such reactive materials, so as to increase the pump capacity by addition of a gettering effect. The sputter-cathodes 56 are arranged so that the cellular passages extending therethrough are substantially perpendicular to the surfaces of the collectors 51. The cellular passages through the sputter-cathodes need not be aligned with the anode cell walls, although such alignment is preferable.

A positive potential with respect to the collector of from 2,000 to 4,000 volts is applied to the anode 52 by means of the high voltage connector 55. A negative potential of between 2,000 and 4,000 volts is applied to the sputter-cathode 56 by means of the bias terminal 58. A magnetic field of from 1,000 to 2,000 gauss is applied to the pump by a magnet 27.

Due to the cellular arrangement of the anode and sputter-cathodes, ions moving from the anode toward the collectors tend to assume a path substantially parallel to the sides of the sputter-cathode passages, and relatively few ions strike the sputter-cathodes. Due to the large potential difference between the anode and the sputter-cathodes, ions approaching the sputter-cathodes are accelerated, and ions striking the sputter-cathode do so with a relatively high velocity. These collisions cause the material of the sputter-cathodes to be sputtered in the direction of the collectors.

Since the ions strike the sputter-cathodes with a glancing or gouging motion, a relatively greater amount of sputtering of material from the sputter-cathodes occurs per collision than occurs when an ion strikes the collector surfaces in a substantially perpendicular direction. Therefore, a smaller number of ions striking the sputtercathodes sputter sufficient material therefrom to replace the over-all loss of material from the collector surfaces due to the sputtering caused by a greater number of ion collisions.

The following details are typical of the construction of an ion pump according to the emboddiment of the invention illustrated in FIG. 5. The ion pump has an anode and two collectors constructed of stainless steel. The sputter-cathode may also be constructed of stainless steel. If air or other gases which may be partially gettered are to be pumped, it is preferable to construct the sputtercathode and collector of a reactive material so as to increase the pump capacity by gettering reactive ions, rather than depending on entrapping alone. The over-all thickness of the pump is 1% inches. The anode and each spotter-cathode are one inch square. The anode has 4 square cells. The sputter-cathode has 36 square cells. The anode is 1 inch thick and each sputter-cathode isMt inch thick. The space between a collector and the adjacent sputtercathode is inch. The space between each sputter-cathode and the anode is inch. A potential positive, with respect to the collector, of 3,000 volts is applied to the anode and a potential negative, with respect to the collector, of 2,000 volts is applied to the sputter-cathodes.

FIG. 6 is a graph of the evacuation pressure obtained with an ion pump constructed with the above dimensions. The substance being pumped is argon. It is to be noted that a substantially constant pressure of approximately -6 mm. Hg exists in the evacuated envelope. The oscillatory characteristic illustrated in FIG. 4 has been eliminated. The minimum pressure shown in FIG. 4 is slightly below the average pressure shown in FIG. 6, indicating that the leak rate of the apparatus whose evacuation characteristic is shown in FIG. 6 was higher than the leak rate of the device whose evacuation characteristic is shown in FIG. 4.

FIG. 7 illustrates another embodiment of the invention. The embodiment of FIG. 7 is particularly useful in devices having magnetic fields which are uniform over a long distance in the direction parallel to the magnetic field. A cylindrical collector 70 is annularly contained within a cylindrical anode 71, an annulus 72 being formed thereby. sputter-cathode replacement material elements 73 extend outward radially from adjacent the collector 70 toward the anode 71.

A high positive potential with respect to the collector is applied to the anode 71. A high negative potential with respect to the collector is applied to the sputter-cathodes 73. Some of the ions moving toward the collector 70 will sputter material from the sputter-cathodes 73 by a process similar to the process described with respect to the device of FIG. 5. The replacement material sputtered from the sputter-cathodes 73 is deposited on the surface of the collector 70, so as to provide continuous entrapment of nonreactive ions pumped therei-nto. A satisfactory nonreaction ion pumping characteristic is thereby achieved.

The alternate embodiment of the invention illustrated in FIG. 8 is especially useful when the magnetic field is uniform but short. It has been found that the density of the ions causing sputtering is normally greatest along the axis of the gaseous discharge. That is, the discharge conforms generally to the outline of each anode cell, and sputtering is greatest opposite the center of the anode cell. In the embodiment of FIG. 8, those portions of the collectors which are aligned with the axis of the dis charge are made transparent. The sputter-cathodes are positioned on the axis of the discharge. Some of the ions, instead of striking the collectors, strike the sputtercathodes and sputter material therefrom. This sputtered material is deposited on the collectors to provide the entrapping layers.

The device of FIG. 8 has an evacuated chamber containing a pair of collectors 81 and a cellular anode 82. A collector terminal 83 passes through the evacuated envelope 80 and is connected to the two collectors 81 by connecting leads 84. The anode 82 is connected by an anode lead 85 to a high voltage connector 86. Each of the collectors 81 has a series of openings 87 aligned with the axis of the discharges of the anode cell. sputter-cathodes 88 are positioned so as to be adjacent the openings 87. The positioning of the sputter-cathodes 88 causes material sputtered therefrom to be deposited on the collectors. The sputter-cathodes 88 are connected by connecting leads to a bias terminal 89 passing through the evacuated envelope 80. An inlet 59' connects the evacuated envelope 80 to the space to be evacuated.

A potential, positive with respect to the collectors 81, is applied to the anode 82 through the high voltage terminal 86. A potential, negative with respect to the collectors 81, is applied to the sputter-cathodes 88 through the bias terminal 89. Ions passing through the collector openings 87 strike the sputter-cathodes 88, causing sputtering. The material sputtered from one sputter-cathode is deposited primarily on the opposite collector and sputter-cathode, due to the almost perpendicular angle at which the sputtering ions strike the sputter-cathode surface. Since the sputter-cahtodes 88 are sputtered to a greater extent than are the collectors 81, due to their placement along the discharge axis, material from the sputter-cathodes is deposited on the collectors at a higher rate than the rate of over-all loss of material from the collectors due to sputtering. Thus, a continuous deposition of an entrapping layer occurs on the collectors, thereby providing a satisfactory non-reactive ion pumping characteristic for the cold-cathode discharge ion pump.

I claim:

1. An improved ion pump of the cold-cathode discharge type comprising an anode having a configuration such that there is a least one plane of symmetry, a collector positioned adjacent the anode, a source of replacement material positioned between the anode and the collector, means for initiating a voltage gradient within at least a portion of the space between the anode and the collector and extending in a direction from the anode toward the collector, means for enclosing said anode, said source and said collector so as to provide a sealed enclosure during pump operation, and means for producing magnetic lines of force through the enclosure wherein the lines extend in a direction from said anode toward said collector, said source of replacement material including an electrode positioned adjacent the collector and disposed so that material is sputtered from said electrode and deposited on the collector by part of the ions pumped when the pump is in operation.

2. An improved ion pump comprising an anode having a configuration such that there is at least one plane of symmetry, a collector adjacent the anode, a source of replacement material positioned adjacent the collector, means for initiating a voltage gradient within at least a portion of the space between the anode and the collector and extending in a direction from the anode toward the collector, an envelope for enclosing said anode, said source and said collector and being in communication with a space to be evacuated, and means for producing magnetic lines of force extending from said anode toward said collector, the replacement material being positioned between the anode and the collector and having a cellular configuration, the axes of the cells of which are substantially perpendicular to the collector.

3. An improved ion pump comprising an anode having a configuration such that there is at least one plane of symmetry, a collector adjacent the anode, a source of replacement material positioned adjacent the collector, means for initiating a voltage gradient within at least a portion of the space between the anode and the collector and extending in a direction from the anode toward the collector, an envelope for enclosing said anode, said source and said collector and being in communication with a space to be evacuated, and means for producing magnetic lines of force extending from said anode toward said collector, the collector being annularly contained within the anode and said source of replacement material comprising a plurality of elements positioned between the surfaces of the anode and collector so as to extend outward radially with respect to the collector.

4. An improved ion pump of the cold-cathode discharge type comprising an anode having a configuration such that there is at least one plane of symmetry, a col lector positioned adjacent the anode, a source of replacement material positioned between the anode and the collector, means for initiating a voltage gradient within at least a portion of the space between the anode and the collector and extending in a direction from the anode toward the collector, means for enclosing said anode, said source and said collector so as to provide a sealed enclosure during pump operation, and means for producing magnetic lines of force through the enclosure wherein the lines extend in a direction from said anode toward said collector.

5. An ionization getter pump wherein ionization of gas takes place in a cold cathode discharge and whose pumping action is based upon cathode sputtering and simultaneous ionization and excitation of gas molecules being pumped comprising a housing having an intake opening for gas to be pumped, an anode disposed within the housing, a pair of electrically conducting collector electrodes disposed within the housing and on either side of the anode, a cathode disposed between the anode and each respective collector electrode and insulated from the anode and each of the collector electrodes in the housing, each of the cathodes comprising a getter substance, the space between the anode and each of the cathodes defining a discharge space, electric connections for passing cathode-sputtering voltage between the anode and the cathodes, magnetic field means for impressing a magnetic field upon the discharge space having field lines extending from one collector electrode toward the other collector electrode, each of the cathodes defining at least one aperture therein having an axis parallel to the magnetic field lines and through which ions from the dis charge space and material sputtered from the cathode pass to the collector electrodes.

6. An ionization pump as defined in claim 5 wherein the anode and each cathode has a cellular configuration.

7. An ionization pump as defined in claim 6 wherein each cathode defines a plurality of cells corresponding to each anode cell, one of the cells of each cathode being aligned with a respective anode cell.

8. An ionization pump as defined in claim 7 including means for initiating a voltage gradient between the anode and the collectors.

9. An ionization pump as defined in claim 8 wherein the anode cathode voltage is greater than the anode collector voltage.

10. An ionization getter pump wherein ionization of gas takes place in a cold cathode discharge and whose pumping action is based upon cathode sputtering and simultaneous ionization and excitation of the gas molecules being pumped comprising a pump housing having an intake opening for gas to be pumped, an anode disposed within the housing, a cathode disposed on each side of the anode within the housing, each of the cathodes comprising a getter substance, the space between the anode and the cathodes defining a discharge space having a discharge axis directed from one cathode through the anode to the other cathode, magnetic field means for impressing a magnetic field upon the discharge space having field lines parallel to said discharge axis, the anode defining at least one aperture therein having an axis parallel to the magnetic field lines, the pump housing forming an electrically conducting surface surrounding the discharge space at least at those sides that extend perpendicular to the magnetic field lines for receiving a portion of the getter substance removed from the cathodes, each of the cathodes defining at least one aperture therein having an axis parallel to said discharge axis and the mag netic field lines, said cathodes extending transversely to the magnetic field lines, electric connections for passing cathode-sputtering voltage between the anode and the cathodes, the anode being electrically insulated from the cathodes and the housing whereby a dilferent voltage may be passed between the anode and the housing than between the anode and cathodes.

11. An ionization pump as defined in claim 10 wherein the anode and each cathode has a cellular configuration, each cathode defining a plurality of cells for each anode cell, a cathode cell being aligned with a respective anode cell.

12. An improved ion pump comprising an anode having a configuration such that there is at least one plane of symmetry, a collector adjacent the anode, a source of re placement material positioned adjacent the collector, means for initiating a voltage gradient within at least a portion of the space between the anode and the collector to provide a gaseous discharge along an axis directed from the anode to the collector, an envelope for enclosing said anode, said source and said collector and being in communication with a space to be evacuated, and means for producing magnetic lines of force extending from said anode toward said collector, the source of replacement material forming sputter surfaces extending toward the anode and defining at least one passageway between said sputter surfaces aligned with the discharge axis and through which ions from the gaseous discharge and material from the sputter surfaces pass to the collector.

13. An ion pump as defined in claim 12 wherein the sputter surfaces comprise a reactive material.

14. An ion pump as defined in claim 12 wherein the sputter surfaces extend substantially parallel to the discharge axis.

15. An ion pump as defined in claim 14 wherein the anode has a cellular construction providing a separate gaseous discharge extending along the axis of each anode cell, the source of replacement material providing openings aligned with each anode cell axis.

16. An ion pump as defined in claim 15 wherein the source of replacement material is a cellulas cathode defining a greater number of cells than the anode with one cathode cell being algned with each anode cell.

17. An ion pump as defined in claim 15 including a collector positioned on each side of the anode and wherein the source of replacement material forms sputter surfaces extending from each collector toward the anode, the magnetic field extending from one collector to the other collector.

18. An ion pump as defined in claim 17 including means for initiating a voltage gradient between the anode and the cathode independently of the voltage between the anode and collector.

19. An ion pump as defined in claim 17 wherein the sputter surfaces comprise a reactive material.

20. An ion vacuum pump comprising a pump envelope adapted to be connected to a enclosure to be evacuated, an anode having a configuration such that there is at least one plane of symmetry mounted within the envelope, a collector surface mounted adjacent the anode, means for producing magnetic lines of force extending in a direction from the anode toward said collector, means including the anode for producing a gaseous discharge in the magnetic field within at least a portion of the space between the anode and the collector for ionizing gases therein by ac celerating electrons within said portion of said region and thereby bombard gas molecules therein, the last means being adapted to produce a potential gradient within said portion of said region for directing at least some of the ions toward the collector surface, a source of replacement material adjacent the collector and forming sputter surfaces extending parallel to the magnetic field lines so that a small portion of the ions traveling toward the collector surface strike the sputter surface at a glancing trajectory and sputter portions of the same onto the adjacent collector surface to continuously deposit an entrapping layer of sputter material on portions of the collector surface into which nonreactive ions are being pumped.

21. An ion pump as denfied in claim 20 wherein the anode has a cellular configuration and the replacement material comprises a cellular cathode, the axes of the cells of the anode and cathodes being substantially perpendicular to the collector and wherein the voltage gradient is impressed between the anode and the cathode.

22. An ion pump as defined in claim 21 wherein the cathode includes a plurality of cells for each anode cell, one of the cathode cells being aligned with a respective anode cell.

23. An ion pump as defined in claim 22 including a pair of collectors positioned on either side of the anode and a cellular sputter cathode positioned between the anode and each collector.

24. An ion pump as defined in claim 23 wherein the sputter cathodes comprise a reactive material.

No reference cited.

WILLIAM L. FREEH, Primary Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent No. 3,535,054 Dated October 20, 1970 Wilson M. Brubaker Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 56, after "thereby" insert increased Column 2, line 30, "thereup" should read thereupon lines 46 and 47, "collectioning" should read collecting Column 3,

line 73, "thesse ion" should read these ions Column 4,

line 20, "ocurirng" should read occurring line 34,

entrapued should read entrapped Column 5, line 42,

"emboddiment" should read embodiment line 65, "10-6" should read 10' Column 9, line 4, "cellulas" should read cellular line 5, "algned" should read aligned Column 10, line 27, cancel "No reference cited." and insert References Cited UNITED STATES PATENTS 2,636,664 4/1953 Hertzler -23069X 2.7Z7,l67 12/1955 Alpert -23069X 2,755,014 Westendorp et a1.--- 2,796,555 6/1957 Connor -230-69X 2,993,638 Hall FOREIGN PATENTS 797,232 Great Britain.

Signed and sealed this 13th day of April 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents FORM PC4050 $59) uscoMM-oc scan-pea ".5. GOVEINMEN" PRINTING OFFICI: II, O:'3!l 

